1. Field of the Invention
The present invention relates to a brake pressure control valve located in the outlet port of a master cylinder for controlling the brake pressure applied to the rear wheels of a motor vehicle, and more particularly to a brake pressure control valve adapted for use with a double piping type hydraulic braking system.
2. Description of the Prior Art
Various kinds of brake pressure control valves are known which control the brake pressure delivered to the rear wheels of the vehicle so that once the master cylinder pressure reaches a certain value (critical pressure), the brake pressure for the rear wheels thereafter increases at a lesser rate than the input pressure from the master cylinder. With this function, the dangerous skid phenomenon wherein the rear wheels are locked prior to the front wheels under braking of the vehicle is prevented.
Now, in order to assure safety of the vehicle, a so-called double piping type hydraulic braking system is widely employed, which includes two groups of brake systems so that even when one system fails to operate, the other system operates to brake the vehicle. The X-piping system and J--J piping system are known as the double piping system.
When the double piping system is employed, two brake pressure control valves become necessary which are respectively mounted in the two (double) hydraulic braking systems. Usually, these two control valves are assembled in a single housing for the purpose of reduction of mounting space and the production cost. Furthermore, for such purpose, it is also usual to use a housing integrated with the master cylinder, such as a tandem master cylinder.
However, most of the brake pressure control valves are constructed to employ the housing as an essential part thereof, so that the operational function of each control valve cannot be expected until the valve is assembled in the housing. In fact, hitherto, the performance test of each valve has been carried out after assembling these two valves in the housing. Thus, when a defect is found in the assembled valve unit, it is necessary to take out the parts of the valves from the housing one by one in an awkward manner. This disassembling work and next-necessitated reassembling work are quite troublesome and thus take a much time.
Apart from the above, in order to adjust or vary the output characteristics of the valve, it has been necessary to provide a number of additional components because each part of the valve is constructed exclusively for a given type valve. In fact, hitherto, for production of various valves having different output characteristics, a number of parts of the same kind but differently formed have been prepared throughout several essential components.
Handling this number of parts is troublesome and thus raises the production cost of the finished valve device.